The present invention relates to the field of backup powering, and more particularly to a means for backing up a computer during mains power failure by powering a volatile memory, preferably by utilizing power over Ethernet.
The growth of local and wide area networks based on Ethernet technology has been an important driver for cabling offices and homes with structured cabling systems having multiple twisted wire pairs. The ubiquitous local area network, and the equipment which operates thereon, has led to a situation where there is often a need to attach a network operated device for which power is to be advantageously supplied by the network over the network wiring. Supplying power over the network wiring has many advantages including, but not limited to; reduced cost of installation; centralized power; and centralized security and management.
Several patents addressed to this issue exist including: U.S. Pat. No. 6,473,608 issued to Lehr et al., whose contents are incorporated herein by reference and U.S. Pat. No. 6,643,566 issued to Lehr et al., whose contents are incorporated herein by reference. Furthermore a standard addressed to the issue of powering remote devices over an Ethernet based network has been published as IEEE 802.3af, whose contents are incorporated herein by reference.
Power over Ethernet (PoE) supplies a limited amount of power to an attached powered device, with the aforementioned standard limiting the average input power of a powered device to a maximum of 12.95 watts. Computers, and in particular desktop computers, are powered by an electrical mains connection and typically draw well in excess of 15 watts. In the event of a failure of mains power the computer power supply maintains power for at least one cycle of mains power, i.e. 17-20 ms. The time period for which power is maintained in the absence of mains power is called the hold up time. At the expiration of the hold up time, computer power is no longer reliably supplied and both the processor state and all information in volatile memory of the computer is lost. Similarly any information stored in video memory, such as fonts being displayed on the screen, is lost. A prior art solution to this difficulty entails supporting each computer with an uninterruptible power supply (UPS), which is designed to reliably supply power for a period of time after loss of mains power. Typically a warning is given by the UPS to the user, enabling the user to store all information in a non-volatile memory and shut down the computer in an orderly fashion. In another prior art solution the UPS is connected by a network connection to the computer, and initiates an orderly shut down of all running programs. Typically the UPS supplies power for a number of minutes enabling an orderly shut down if prompt action is taken.
The provision of a UPS for each computer is costly and requires additional space at each computer location. Furthermore, maintenance of a separate UPS at each computer adds to overhead. Alternatively a centralized UPS is provided supplying power over dedicated AC wiring to each computer to be supported. Such a dedicated wiring is costly to install and expensive to modify when changing the location of computers.
Modern computers are designed with certain power saving features as exemplified in the advanced computer power interface (ACPI) standard. In particular, standby modes or sleeping states are defined in which information including all registers defining the processor's state are stored in volatile memory. Power is subsequently shut down to the processor, hard drive and monitor with power being supplied exclusively to a standby memory power bus. Such a mode of operation is defined for example in the Intel ACPI 3.0 standard. In order to achieve an Energy Star rating from the U.S. Environmental Protection Agency computers must consume significantly reduced power in a standby mode. In order to meet U.S. Government Guidelines as embodied in an Executive Order dated Jul. 31, 2001, appliances including computers to be purchased by the U.S. Government are preferably to consume less than 1 watt in standby.
An exemplary embodiment of a computer architecture supporting ACPI 3.0 is illustrated in FIG. 1. Computer 10 comprises: a power supply unit 20 comprising a controlled power supply 22 and a standby power supply 24; a CPU 30; a hard drive 40; a volatile memory 50; an ORing circuit 60; a standby power bus 65; and an AC mains connection 70. Power supply 20 receives power from AC mains connection 70 and controlled power supply 22 of power supply unit 20 is responsive to an output signal from CPU 30 labeled PS_ON# as will be explained further hereinto below. Controlled power supply 22 outputs a plurality of voltages including 5 volts, 3.3 volts and 12 volts. Standby power supply 24 output a separate 5 volt output, labeled 5V STBY which is unaffected by the state of PS_ON#. The 5 volt output is fed to CPU 30 and hard drive 40 and is connected to one input of ORing circuit 60. The 5 volt standby output is connected to a second input ORing circuit 60, and the output of ORing circuit 60 is connected to volatile memory 50 via standby power bus 65. Other devices may receive power from the standby power supply 24 as well.
In operation, when AC mains power is available from AC mains connection 70 and responsive to a active low signal PS_ON#, power is supplied via the plurality of power outputs of controlled power supply 22 to CPU 30 and hard drive 40. Power is further supplied via the 5 volt output of controlled power supply 22 through ORing circuit 60 to volatile memory 50 over standby power bus 65. In the event that a logic high signal appears on PS_ON#, controlled power supply 22 responsive to the logic high signal removes power from the 5 volt output, the 3.3 volt output and the 12 volt output. However power is still supplied via standby power supply 24 via ORing circuit 60 to volatile memory 50 and any other devices connected to the 5 volt standby line. Furthermore devices requiring other voltages that are supplied exclusively from controlled power supply 22 are not powered unless a dual supply arranged is provided. Such an arrangement is well known to those skilled in the art and is commercially available, for example via the use of a Fairchild FAN5063 Dual Switch Controller available from Fairchild Semiconductor of South Portland, Me.
In computers designed to support this architecture power supply 20 is responsive to the PS_ON# signal generated by CPU 30, and in particular by a power management interface (not shown) of a chip set associated with CPU 30. Thus, to proceed to a standby mode, CPU 30 first acts to store all information including status registers in volatile memory 50 prior to setting the value of PS_ON# to high. In one embodiment this is accomplished by enabling a system management mode (SMM). Unfortunately, in the event of a loss of AC mains power, CPU 30 lacks sufficient time and warning to proceed to the standby mode in an orderly fashion, as the hold up time of 17-20 milliseconds is insufficient. Furthermore, no mechanism is supplied to initiate the standby mode in the event of a loss of AC mains power. Additionally, in the event of a loss of AC mains power, there is no source of electrical power to maintain power bus 65.
The above has been described as utilizing an ORing circuit 60, however this is not meant to be limiting in any way. In particular, in one embodiment ORing circuit 60 is replaced with a plurality of FET switches in series, the first of the FET switches feeding power to memory 50 and to the input of subsequent switches. Such an embodiment is described in U.S. Pat. No. 6,523,125 issued Feb. 18, 2003 to Kohno et al entitled “System and Method for Providing a Hibernation Mode in an Information Handling System”, the entire contents of which is incorporated herein by reference. In another embodiment ORing circuit 60 comprises a dual switch controller such as the Fairchild FAN5063 described above.
FIG. 1b is a high level schematic diagram illustrating a chipset system block diagram of computer 10 supporting the advanced configuration power interface according to the prior art. Computer 10 comprises CPU 30; a northbridge 80; volatile memory 50; a video interface 85; a southbridge 90; IDE devices 94; USB ports 96; serial ports 98; and audio and UARTs 99. The operating system running on computer 10 implements the ACPI and controls power useage of each of the connected devices including that of CPU 30. Northbridge 80 interfaces directly with a processor system bus of CPU 30 and is connected thereto. Video interface 85, which in one embodiment may comprise one or more of: a cathode ray tube display; a digital video output; a low voltage digital signal interface; and an accelerated graphics port interface, is connected to northbridge 80. Volatile memory 50, which in an exemplary embodiment comprises synchronous dynamic random access memory is connected to northbridge 80.
Southbridge 90 is connected to northbridge 80 and has connected thereto IDE devices 94; USB ports 96; serial ports 98; and audio and UARTs 99. Thus, northbridge 80 communicates directly with CPU 30, and southbridge 90 communicates with CPU 30 via northbridge 80. The ACPI is operable to control power useage of each of the connected devices and to place any of the devices in computer 10, including CPU 30 into a reduced power consumption mode.
Unfortunately, the ACPI is unable to reduce power consumption in the event of a mains power failure, as operating power for computer 10 is not supplied. Furthermore, in the event of a mains power failure, power is not supplied for volatile memory 50, and thus in the absence of supplied power all information stored thereon is lost.
The above has been described in relation to a computer exhibiting a northbridge/southbridge architecture, however this is not meant to be limiting in any way. Other architectures, specifically including an Intel Hub Architecture exhibit similar issues regarding powering and loss of information and processor state upon AC mains failure.
What is needed, and not supplied by the prior art, is an automatic means for preventing the loss of information in a computer during a power failure while not requiring a UPS or other large battery back up system.